Microstructural characterization of electron beam-physical vapor deposition thermal barrier coatings through high-resolution computed microtomography

Abstract

Thermal barrier coatings (TBCs), deposited using the electron beam-physical vapor deposition (EB-PVD) process, comprise a unique architecture of porosity capable of bridging the technological gap between insulation/life extension and prime reliance. The TBC microstructures consist of columnar structure, nucleated via vapor condensation, along with a high degree of intercolumnar porosity, thus providing enhanced stress relief on thermomechanical loading and also accommodating misfit stresses resulting from CTE mismatch. In this article, we report the characterization of these coatings using high-resolution synchrotron-based X-ray computed microtomography (XMT) at 1.3-m resolution. Experiments focused on quantitative characterization/visualization of imperfections in these coatings and on the relative changes in microstructural features upon isothermal annealing. The influence of time/temperature of exposure was investigated and the results were correlated with elastic modulus.

Recent advances in X-ray microtomography applied to materials

“…Highly non-equilibrium solidification occurs in spray deposition of thermal barrier coatings, and synchrotron microCT is invaluable for determining pore shapes and for quantifying pore volume fraction in the coating as a function of distance from the substrate. [486][487][488][489] Different processes produced different pore shapes that can be directly visualised and compared with the results of techniques such as small angle neutron scattering (SANS) and nanoindentation for elastic moduli determination. 486,489 Gradients in porosity have also been correlated with indentation derived moduli and SAXS.…”

“…486,489 Gradients in porosity have also been correlated with indentation derived moduli and SAXS. 487,488 MicroCT characterisation of vapour phase processed materials does not appear to have received much attention since the first IMR review. Bernard and coworkers reported some results of isobaric chemical vapour infiltration of a C/C composite.…”

Application of synchrotron x-ray microtomography to investigate ductile fracture in Al alloys

“…7,8 It has many applications in a variety of fields, such as for the identification of internal material inhomogeneities, assessment of internal defects and damage, and investigation of the microstructure-property relationships in various materials. [9][10][11][12][13][14][15] The X-ray microtomography is also expected to have a good perspective in fracture studies, however, a particularly high spatial resolution well suited for the investigation of crack and crack/microstructure interaction is much required. 16,17 Fortunately, the currently largest third-generation synchrotron radiation facility at the SPring-8 in Japan enables X-ray computed tomography with a high resolution down to less than 1 m.…”